Itinerant magnetism of disordered Fe-Co and Ni-Cu alloys in two and three dimensions

The electronic structure and band magnetism of disordered ${\mathrm{Fe}}_{100\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$ and ${\mathrm{Ni}}_{100\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cu}}_{\mathit{x}}$ bulk alloys and of corresponding disordered overlayers on an fcc Cu(001) substrate were studied by means of the first-principles tight-binding linear muffin-tin orbital coherent potential approximation method. For the Fe-Co system, we found that the composition dependence of the averaged and the local Fe magnetic moments is strongly affected by the dimensionality of the system while the local Co moments remain nearly constant. In the bulk bcc alloys, a nonmonotonic behavior of the averaged magnetization occurs due to the transition from weak to strong ferromagnetism. The averaged magnetization of the random overlayers depends linearly on the composition while the local Fe and Co moments are constant since the strong ferromagnetism is stabilized by the substrate throughout the whole composition range. For the Ni-Cu system, a transition from ferromagnetism to paramagnetism is found both in the bulk fcc alloys and in the overylayers. The ferromagnetism of the overlayers is reduced in comparison to the bulk systems of the same composition. The concentration trends of local densities of states, local numbers of electrons, and work functions are discussed.